In conventional X-ray CT apparatuses, it is necessary to previously make a scan plan before actually starting data acquisition by a main scan, such as a dynamic scan. In the scan plan, X-ray tube voltage, X-ray tube current, slice thickness, a cone angle, a fan angle, a gantry tilt angle, a reconstruction matrix, a main scan position, and a main scan range from a scan start position to a scan end position to be used in the main scan are set. In order to set main scan conditions, such as the main scan position and the main scan range, in the scan plan, a scanogram scan (prescan) is performed, while a table-top on which a patient is placed is moved in a body axis direction of the patient, with rotation of an X-ray tube and a detector stopped. When scanograms are obtained by the scanogram scan, the main scan conditions, such as the main scan position and the main scan range, are designated using these scanograms. Therefore, it is necessary to irradiate an X-ray to the patient at a stage of the scan plan, and there is a disadvantage that an amount of exposure of the patient to radiation increases.
Therefore, an X-ray CT apparatus that can be easily operated, while suppressing unnecessary exposure of the patient to radiation at the stage of the scan plan, is proposed. This X-ray CT apparatus has a bed mechanism, an X-ray source, a detector, a gantry, a position setting unit, a positional relationship detecting unit, and a scanogram scan control unit. The bed mechanism has a table-top on which the patient is placed and which is movable in a body axis direction of the patient. The X-ray source is for irradiating an X-ray to the patient. The detector is for detecting the X-ray transmitted through the patient. The gantry is located so that the X-ray source and the detector rotate, being opposed to each other, with the patient sandwiched between them. The position setting unit sets any positions of the patient or the table-top for designating a plurality of regions of the patient. The positional relationship detecting unit detects positional relationships between the plurality of regions and the gantry, based on the set positions. The scanogram scan control unit continuously obtains scanograms for each of the plurality of regions by performing a scan, while moving the table-top, while switching irradiation and stop of an X-ray from the X-ray source, based on the detected positional relationships.
In addition, there is a case where alignment is performed by irradiating laser light to a portion corresponding to a center line of an X-ray irradiation range of the main scan, using a projector, in patient setting in an X-ray CT apparatus. In this case, the projector indicates only the center line of the X-ray irradiation range at a main scan position, and therefore, a health professional cannot accurately recognize the X-ray irradiation range, for example, when the main scan is performed using a multi-slice detector.